Molecular Dynamics in a Chiral Smectic Liquid Crystal Studied by 13C-Nuclear Magnetic Resonance Spin-Lattice Relaxation Time Observation

概要

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In order to study molecular rotation around its long axis in chiral smectic phases, the temperature dependence of the spin-lattice relaxation time $T_{1}$ is investigated in an antiferroelectric liquid crystal, ($S$)-4-(1-methylheptyloxy-carbonyl)phenyl 4$'$-octyloxybiphenyl-4-carboxylate ($S$-MHPOBC) by means of solid-state 13C-NMR spectroscopy. The spin-lattice relaxation time $T_{1}$ of the aromatic core part has a minimum at about 95°C in its temperature dependent curve. Since $T_{1}$ minimum occurs under a condition of $\omega_{0}\tau_{\text{c}}\sim 1$, the correlation time $\tau_{\text{c}}$ of molecular motion should be of the order of $2\pi/\omega_{0}\sim 10^{-8}$ s here, with the Larmor frequency $\omega_{0}$ of 100 MHz in the present measurements. The temperature dependence of $T_{1}$ reveals that the activation energy in the SmC$_{\text{A}}^{*}$ phase is larger than that in SmA for most of the carbon nuclei of the aromatic core part. It suggests that the molecular rotation is hindered in the SmC$_{\text{A}}^{*}$ phase, in which the large spontaneous polarization exists in a layer.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2003-06-15